A first step in SMT process that is used for assembling an electronic substrate starts from supplying on the substrate an appropriate quantity of the solder paste formed by mixing a flux with solder powders. There is a method referred to as a screen printing one of the methods of supplying the solder paste on the substrate.
FIGS. 10A, 10B, 10C, 10D, 10E and 10F are motion illustration diagrams showing an example of a conventional screen printing. In the screen printing, as shown in FIG. 10A, a screen 104 made of a steel plate in which apertures 103 are formed with them being aligned with electrodes 102 of a substrate 101 and the substrate 101 are closely contacted to each other, as shown in FIG. 10B.
The solder paste S is put on the screen 104, as shown in FIG. 10C, and sliding a squeegee 105 toward a direction of an arrow F with it closely contacting the screen 104, the solder paste S is filled in the apertures 103 as shown in FIG. 10D. Next, by scraping the excessive solder paste S off using the squeegee 105, the solder paste S is filled in only the apertures 103 of the screen 104, as shown in FIG. 10E.
Thereafter, as shown in FIG. 10F, by separating the screen 104 and the substrate 101 from each other, the solder paste S filled in the apertures 103 of the screen 104 is transferred to a side of the substrate 101.
The screen printing has been popularized as a method of allowing the solder paste to be accurately supplied at a lowest price when consecutively producing the substrates of same type. It also has maintained its position as the method of allowing the solder paste to be supplied to a portion to be soldered which has been extremely minimized and/or narrowed connection with miniaturization of the substrate and pitch narrowing of the electrodes.
By the way, in the SMT process, the supply of the solder paste is performed in its first step and then, a component mounting steps and then a soldering step by heating follow. If any faults occur in supplying the solder paste, these faults in supplying it cannot be covered even when the following component mounting step and the following soldering step by heating are performed under best conditions.
Accordingly, it is considered that the supply of the solder paste is the most important step in the SMT process. As a measure against the faults when printing, any optimization of viscosity of the solder paste and a size of the solder powder, any optimization of a printing condition and/or the like have been studied in the past and a printing process, though not quite satisfactory, is being fixed.
On the other side, on the assembly of electronic device, there is a printing process referred to as a film method as a method of forming solder bumps on the device, particularly. FIGS. 11A, 11B, 11C, 11D, 11E and 11F are motion illustration diagrams showing an example of a conventional film method.
In the film method, as shown in FIG. 11A, a film 106 is attached onto the substrate 101 and as shown in FIG. 11B, apertures 107 are formed in the film 106 by removing therefrom portions to which the solder paste should be supplied using etch.
By sliding the squeegee 105 with it closely contacting the film 106 while, as shown in FIG. 11D, the solder paste S is put on the film 106, the solder paste S is filled in the apertures 107 as shown in FIG. 11C. Next, by scraping the excessive solder paste S off using the squeegee 105, the solder paste S is filled in only the apertures 107 of the film 106.
Next, the substrate 101 is put into a reflow furnace while the film 106 is attached thereto and as shown in FIG. 10E, solder bumps 108 are formed. Thereafter, as shown in FIG. 11F, the film 106 is removed from the substrate 101 using a parting agent.
In the above-mentioned screen printing, the solder paste may remain in the apertures of the screen when separating the screen from the substrate in a case where the pitch narrowing of the electrodes advances and the apertures formed in the screen is made extremely small so that it will remove from the substrate. This fails in filling an inadequate amount of solder. In the film method, in contrast, by removing the film after the solder paste is fused and the solder bumps are formed, the solder bumps are formed on a side of the electrodes of the substrate so that an amount of the solder is fixed.
On the other hand, in a field of the screen printing, a technology has been proposed such that after embrocation as paste or ink is printed on printing materials by a squeegee under atmospheric pressure, the printing materials are put under predetermined high vacuum to generate air bubbles and the generated air bubble is scraped off by the squeegee as well as the printing materials return to the atmospheric pressure to further break down the air bubbles so that any air bubbles can be removed from the embrocation (for example, see Patent Document 1).